Syrian forces killed at least 56 people in the past 24 hours in the province of Idlib in violence raging ahead of the start of a mission to monitor President Bashar al-Assad's implementation of an Arab League peace plan, activists said on Wednesday.

The escalating death toll in nine months of popular unrest has raised the spectre of civil war in Syria with Assad still trying to stamp out protests with troops and tanks despite international sanctions imposed to push him onto a reform path.

The British-based Syrian Observatory for Human Rights said it had the names of 56 civilians and activists killed in Idlib's Jabal al-Zawiyah region on Tuesday and the death toll could be as high as 121.

Idlib, a northwestern province bordering Turkey, has been a hotbed of protest during the revolt against Assad, inspired by uprisings across the Arab world this year, and has also seen escalating attacks by armed insurgents against his forces.

The Observatory said rebels had damaged or destroyed 17 military vehicles in Idlib since Sunday and killed 14 members of the security forces on Tuesday in an ambush in the southern province of Deraa, where anti-Assad protests began in March.

Events in Syria are hard to verify because authorities have banned most independent reporting. But Tuesday's bloodshed brought the death toll reported by activists in the last 48 hours to over 200, reinforcing fears of a slide into civil war.

The main opposition Syrian National Council said 250 people had been killed on Monday and Tuesday in bloody massacres, and called for the Arab League and United Nations to act to protect civilians.

It demanded an emergency U.N. Security Council session to discuss the (Assad) regime's massacres in (Jabal al-Zawiyah) and Homs, in particular and called for safe zones to be set up under international protection.

It also said Jabal al-Zawiyah, Idlib and Homs should be declared disaster areas and urged the International Red Crescent and other relief organisations to provide humanitarian aid.

ARAB LEAGUE MONITORS

Arab League Secretary-General Nabil Elaraby said on Tuesday that an advance observer team would go to Syria on Thursday to prepare the way for 150 monitors due to arrive by end-December.

Syria stalled for weeks before signing a protocol on Monday to admit the monitors, who will check its compliance with the plan mandating an end to violence, withdrawal of troops from the streets, release of prisoners and dialogue with the opposition.

In a week's time, from the start of the operation, we will know (if Syria is complying), Elaraby said.

Syrian pro-democracy activists are deeply sceptical about Assad's commitment to the plan, which, if implemented, could embolden demonstrators demanding an end to his 11-year rule, which followed three decades of domination by his father.

France said it hoped the monitors could carry out their mission quickly. But it also said Assad had a record of broken pledges and that Monday's violence showed there isn't a moment to lose.

For months we have seen Bashar al-Assad not keep to commitments he made to his people and he has increased his efforts to play for time in the face of the international community, Foreign Ministry spokesman Bernard Valero said.

In recent months, peaceful protests have increasingly given way to armed confrontations, often led by army deserters.

Some opposition leaders have called for foreign military intervention to protect civilians from Assad's forces.

In a show of military power, state television broadcast footage of live-fire exercises held by the navy and air force, which it said aimed at deterring any attack on Syria.

U.N. TOLL

The United Nations has said more than 5,000 people have been killed in Syria since anti-Assad protests broke out in March, encouraged by other street uprisings in the Arab world that have overthrown dictators in Tunisia, Egypt and Libya to date.

Several weeks ago Damascus said 1,100 members of the security forces had been killed by armed terrorist gangs. The armed insurrection against Assad has gathered pace since then.

Syria agreed to the Arab peace plan in early November, but the violence continued, prompting Arab states to announce financial sanctions and travel bans on Syrian officials.

The United States and European Union have imposed sanctions on Syria, which combined with the unrest itself have sent the economy into a sharp decline. The Syrian pound fell nearly 2 percent on Tuesday to more than 55 pounds per dollar, 17 percent down from the official rate before the crisis started.

Arab rulers are keen to prevent a descent into civil war in Syria that could infect a region already riven by rivalry between non-Arab Shi'ite Muslim power Iran and Sunni Muslim Arab heavyweights such as Saudi Arabia.

(Editing by Mark Heinrich)